HOMEBREW Digest #5425 Wed 01 October 2008

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  pH and temperature ("A.J deLange")
  Brix and Plato ("A.J deLange")
  Re: Mash Temp and Color (Kai Troester)
  acid bath for wort chiller? (Jon Fischer)

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---------------------------------------------------------------------- Date: Tue, 30 Sep 2008 08:55:45 -0400 From: "A.J deLange" <ajdel at cox.net> Subject: pH and temperature RE: "... no practical ways (for the home brewer) to measure the mash pH ant mash temp. Both strips and meters are designed to measure pH of a cooled sample. And the ATC feature of a pH meter doesn't compensate for the pH shift of the mash." The second part of the statement is true enough - ATC does not account for pH shift (which is caused by the temperature dependence of the pK's, which are measures of the energy required to remove protons from the acids in the mash). It merely accounts for the the fact that the response of the electrode is E0 + (R*T/F)*log[H+] with E0, R and F being constants, T the temperature and [H+] the hydrogen ion activity (concentration) which does in fact change with temperature through the pK's as mentioned above. Apologies to Chad for logs 2 days in a row. It is very important that people understand that there are two distinct mechanisms: a) the shift in actual pH with temperature and b) the change in the response of a pH electrode with temperature to whatever pH is encountered. Now the first part of the statement is not quite true. Today's meters are generally capable of measurement at mash and even kettle temperatures. The instructions that came with your meter or electrode should specify the range of temperatures that it can handle. Referring to the points above if you dunk your electrode into the mash tun or kettle you will read the pH at the temperature of the mash or wort provided that your meter is ATC equipped as nearly all are these days. If you remove a sample from the same mash or wort and cool it to room temperature you will note a rise of a couple of tenths of a point as the mash or wort cools. Despite the opinion of giants in the industry such as Jean DeClerck that "..the pH should be measured at the temperature of the reaction." [Vol. I p267] it is usual to measure at laboratory temperature and the ASBC Method for pH determination of worts prescribes this. The clear advantage of doing so is that variation in measured pH over the course of a mash/boil cycle are those caused by the chemistry of the mash and are not masked by the fact that, for example, a protein rest was done at 124 F and a saccarification rest at 149. A not so obvious advantage is that the working part of most electrodes is still a very delicate, very thin glass bulb which is subject to considerable thermal stress as it is thrust into boiling wort or hot mash and again when it is remove to cool air. This was posted here years ago by someone who was involved in the manufacture of these things, as I recall. I can personally testify that since I have started taking all measurements at room temperature my electrodes last much longer and at the prices they command that is definitely a good thing. A.J. Return to table of contents
Date: Tue, 30 Sep 2008 09:16:34 -0400 From: "A.J deLange" <ajdel at cox.net> Subject: Brix and Plato The work of the Normaleichungskomission under Dr. Plato was undertaken in order to correct the Brix tables to Teutonic levels of precision. The Brix tables in turn represent an improvement on the original work of Balling. In all three cases the object was to obtain values of specific gravities for solutions of sucrose of given strength by weight (i.e. 10 P or 10 Brix represents 10 grams of sucrose in 100 grams of solution). The reference temperatures for the specific gravities were different but when reduced to the same reference temperature the differences between the Brix specific gravities and Plato specific gravities are in the 5th and 6th decimal places. At the level at which refractometers and hydrometers work, Brix and Plato are, thus, the same. A.J. Return to table of contents
Date: Tue, 30 Sep 2008 10:39:17 -0400 From: Kai Troester <kai at braukaiser.com> Subject: Re: Mash Temp and Color Kevin, > I made two experimental 3 liter batches of about 10 deg P OE this > weekend. Both were > 100 percent Maris Otter. I mashed one at 65 deg C (149 deg F) and the > second at > 70 deg C (158 deg F). All other variables, as best I could control, > were kept the same. > (OEs were 10.4 and 10.6 deg P). Interestingly the wort from the low temp > mash was > noticeably darker than the high temp mash. I was not expecting the > difference, but > should I have? They are in 1 gallon jugs so the difference is unmistakable. How much darker are we talking about here? Did you measure the wort pH? I expect it to be about the same as I expect that you used the same water for both batches. One cause that I can think of is that the lower temperature mash created more simple sugar and amino acids than the higher temperature. These are the the compounds that react to during maillard reactions. In addition to that, maybe the pH of the higher temp mash dropped further due to the increased reaction between calcium/magnesium and malt phosphates. Decoction mashes are known to lower the pH further as a result the increased precipitation of phosphates. Kai Return to table of contents
Date: Wed, 1 Oct 2008 11:21:47 -0700 (PDT) From: Jon Fischer <fischjon at yahoo.com> Subject: acid bath for wort chiller? Hello Friends, I have been using a flat plate counter flow wort chiller with great success until I recently noticed a drop in performance. I am trying to clean it, based on the manufacturer's advice which includes a soak in 5% food grade acid such as citric or phosphoric. Would any of you recommend that I use a 5% solution of "Star San"? If so, how should I make a 5% solution. Thanks, Jon Fischer Columbus, Indiana Return to table of contents
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